The invention relates to a coldforming, i.e. coldrolling, machine in accordance with the preamble of claim 1, a rolling rack suited for coldforming machines of such type and a method of coldforming a workpiece.
In the case of such coldforming machines the workpiece to be machined is rotatably clamped between two live centers or other quick-acting chucking devices, wherein usually a feed axis is allocated to said workpiece chucking device. The desired profile is imparted to the workpiece through two synchronous opposed directional coldrolling racks which simultaneously engage the workpiece and start rotation initially by frictional engagement and later by positive locking. The material flows into the free spaces of the tool, i.e. of the rolling racks. Normally the height of the ground profile of the rolling rack increases in the shaping area so that each racktooth presses successively deeper into the workpiece than the preceding one. Upon reaching the full profile depth, there can follow a calibrating zone and a stress relieving zone along which the geometry and the surface quality of the workpiece are optimized.
This non-cutting coldforming of profiles, such as e.g. serrations (straight or angular), spiral teeth, oil grooves, threads or knurls is about 30 times faster than the cutting machining of the profiles. Coldformed workpieces have in addition a higher strength, a better surface finish and a high accuracy.
In the applicant's brochure “Special machine series XK” a coldforming machine is presented in which the two opposed directional rolling racks are arranged in horizontal direction, while the axis of the workpiece is arranged likewise in horizontal direction transversely to the direction of movement of the racks. What is a drawback with this solution is that a considerable overall width of the coldforming machine is required due to the horizontal arrangement of the rolling racks. This known machine has in addition a hydraulic drive whose hydraulic unit requires very much space.
This drawback is eliminated by a coldforming machine in accordance with WO 99/43454 A1 in which the rolling racks are disposed in vertical direction so that the machine requires a considerably smaller mounting area.